CO₂/CH₄, CH₄/H₂ and CO₂/CH₄/H₂ separations at high pressures using Mg₂ (dobdc)

Abstract

High-pressure separations of binary and ternary mixtures of CO₂, CH₄ and H₂ are relevant to carbon dioxide capture as well as hydrogen and natural gas purification. Metal–organic frameworks represent a class of porous materials that could be used to accomplish these separations, and Mg₂ (dobdc) (dobdc⁴⁻ = 1,4-dioxido-2,5-benzenedicarboxylate), also sometimes referred to as Mg–MOF-74 or CPO-27–Mg, is an especially lightweight metal–organic framework with a high concentration of coordinatively-unsaturated metal sites decorating its interior surfaces. High pressure CH₄ adsorption isotherms presented here, together with CO₂ and H₂ adsorption behavior, are analyzed using the Ideal Adsorbed Solution Theory to model CO₂/CH₄, CH₂/H₂ and CO₂/CH₂/H₂ mixture separations using Mg₂ (dobdc). The selectivities, working capacities and breakthrough performances for these three mixtures are reported, and Mg₂ (dobdc) is shown to outperform zeolite 13X in each scenario.